PHILADELPHIA — A doctor who was responsible for cutting the spines of babies after botched abortions was convicted Monday of three counts of first-degree murder in a case that became a sharp rallying cry for anti-abortion activists.

The doctor, Kermit Gosnell, 72, operated a clinic in West Philadelphia catering to poor women that prosecutors called a “house of horrors.”

The case turned on whether the late-term pregnancies Dr. Gosnell terminated resulted in live births. His lawyer, Jack McMahon, argued that because Dr. Gosnell injected a drug in utero to stop the heart, the deliveries were stillbirths, and movements that witnesses testified to observing — a jerked arm, a cry, swimming motions — were mere spasms.

But after deliberating 10 days, the jury found Dr. Gosnell guilty in the deaths of victims known as Baby A, Baby C and Baby D. He was found not guilty of murdering Baby E.

Prosecutors have said they will seek the death penalty when the trial moves into the sentencing phase next Tuesday.

While abortion rights groups argued that Dr. Gosnell operated far outside the legalities and norms of women’s health care, abortion opponents seized on the case to raise questions about the ethics of late-term abortions. Put simply, they asked why a procedure done to a living baby outside the womb is murder, but destroying a fetus of similar gestation before delivery can be legal.

“What we need to learn from the Gosnell case is that late-term abortion is infanticide,” the Daily Beast columnist Kirsten Powers wrote last week, after starting an online furor earlier with a column suggesting that the news media had ignored the case for ideological reasons.

Abortion rights supporters said it was opponents who politicized the trial. What abortion opponents really sought from the trial, they said, was an acceleration of restrictions at the state level to effectively end legal abortion.

“Justice was served to Kermit Gosnell today and he will pay the price for the atrocities he committed,” Ilyse Hogue, president of Naral Pro-Choice America, said in a statement. “Anti-choice politicians, and their unrelenting efforts to deny women access to safe and legal abortion care, will only drive more women to back-alley butchers like Kermit Gosnell.”

In recent weeks, the case was cited in Congress to support restricting abortions past 20 weeks of pregnancy, and it was invoked by an anti-abortion political action committee in radio ads to attack the Democratic candidate for governor of Virginia, Terry McAuliffe.

Although the trial has not brought new issues or tactics to America’s long-running abortion wars, it provided an emotional jolt through five weeks of graphic testimony and an earlier grand jury report.

“This is a visual argument that no one would ever want to have,” said Marjorie Dannenfelser, president of the Susan B. Anthony List, which works to elect women opposed to abortion. “But if we’re going to have it, let’s go ahead and have it. What are the limits? What are we as a society willing to forbear?”

She and others predicted greater support for laws banning abortions past 20 weeks, which have been adopted in several states in recent years, on the disputed theory that fetuses of that age feel pain. Dr. Gosnell was found guilty of 24 counts of performing an abortion beyond 24 weeks, the limit in Pennsylvania.

Opponents of the restrictions argue that later abortions are very rare: fewer than 1.3 percent are past 20 weeks of gestation, according to the Centers for Disease Control and Prevention. Abortion rights activists say restrictions before fetal viability, generally 24 weeks, violate the constitutional protections of Roe v. Wade.

Nonetheless, “the imagery” of later abortion “is very powerful,” said Elizabeth Nash, state issues manager for the Guttmacher Institute, a research group that supports abortion access. “In 2010 Nebraska banned abortion at 20 weeks post-fertilization,” she said. “That bill was seen as the type of bill that was going to catch fire across the country. It did.”

Dr. Gosnell was also convicted of involuntary manslaughter in the death of a 41-year-old patient, Karnamaya Mongar, who died of an overdose of sedatives. Among lesser charges, he was found guilty of 211 counts of not waiting 24 hours after consulting with a patient before performing an abortion.

Activists on both sides debated whether the deplorable conditions at Dr. Gosnell’s clinic — including broken equipment, bloodstained recovery chairs and an untrained staff giving anesthesia and other drugs — could be found at other clinics.

Anti-abortion groups cited the case to press for more regulations of clinics. “By pulling back the secrecy that cloaks this industry that preys on women’s misery, we have a real agenda moving forward,” said Charmaine Yoest, the president of Americans United for Life, which pushes for stricter clinic rules.

But abortion rights groups attacked the regulations as a backdoor route to shut clinics by requiring costly but medically unneeded upgrades, like wider hallways and bigger closets.

“What’s going on with these laws is really about the agenda of having abortion eventually made illegal again,” said Nancy Northup, president of the Center for Reproductive Rights in Washington, which has challenged the laws in court. “And if that were to happen, unfortunately you’d have a lot more Gosnells out there.”

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Jack McMahon, Dr. Kermit Gosnell’s lawyer, on Monday in Philadelphia. Dr. Gosnell was found guilty of first-degree murder.CreditRyan Collerd for The New York Times

The scathing grand jury report in 2011 on Dr. Gosnell’s clinic, the Women’s Medical Society, on Lancaster Avenue, detailed how despite complaints and malpractice suits, no inspector had visited in 16 years. The clinic was raided only after a tip that it operated as an illegal prescription mill. A month after the report, Gov. Tom Corbett fired six employees of the Health and State departments.

In the witness box, clinic employees said live births occurred regularly, and they believed Dr. Gosnell’s explanation for snipping necks with surgical scissors — to “ensure fetal demise” — was accepted practice in late-term abortions. An abortion doctor who testified for the prosecution said such practice was unheard of.

One witness, Steven Massof, testifying under a plea agreement to avoid first-degree murder charges, instructed jurors to feel the backs of their own necks and said, “It’s like a beheading.”

Another former employee, Adrienne Moton, sobbed as she described the death of Baby A, aborted when his teenage mother was about 29 weeks pregnant. Ms. Moton was so upset she took a cellphone photograph of him, which was shown in court. She said Dr. Gosnell had joked that the baby was big enough to walk to a bus stop.

Ms. Moton, who also testified under a plea agreement, said she cut the neck of Baby D, who was delivered into a toilet while its mother, given a large dose of a drug to dilate the cervix, waited for Dr. Gosnell to arrive.

Another clinic worker said she followed Dr. Gosnell’s instructions and cut the neck of Baby C after it moved an arm. The doctor told her was an “involuntary movement.”

Dr. Gosnell was originally charged with seven counts of first-degree murder, but Judge Jeffrey P. Minehart of Common Pleas Court earlier threw out three other cases of infants said to have been born alive, known as Baby B, Baby F and Baby G.

Several weeks into the trial, which began March 18, anti-abortion activists and some conservative commentators accused the national news media of skipping it, a charge amplified across social media.

On April 15, President Obama’s spokesman was asked if he was following the trial. “The president is aware” of the case, said Jay Carney, the White House spokesman.

Even as reporters from national newspapers arrived in Courtroom 304 of the Criminal Justice Center, a blog war continued between abortion-rights supporters, who had written of Dr. Gosnell’s abuses from the time of his indictment, and conservatives, who continued to fault broadcast television for a “blackout.”

On Monday, there were 29 reporters in the courtroom and a row of television crews on the sidewalk.

Jon Hurdle reported from Philadelphia, and Trip Gabriel from New York.

A version of this article appears in print on , Section A, Page 12 of the New York edition with the headline: Philadelphia Abortion Doctor Guilty of Murder in Late-Term Procedures. Order Reprints | Today’s Paper | Subscribe